In conventional radio frequency (RF) plasma processing, such as that used during stages of fabrication of many semiconductor devices, RF energy may be provided to a substrate process chamber via an RF energy source. The RF energy may be generated and provided in continuous or pulsed wave modes. Due to mismatches between the impedance of the RF energy source and the plasma formed in the process chamber, RF energy is reflected back to the RF energy source, resulting in inefficient use of the RF energy and wasting energy, potential damage to the process chamber or RF energy source, and potential inconsistency/non-repeatability issues with respect to substrate processing. As such, the RF energy is often coupled to the plasma in the process chamber through a fixed matching network that operates to minimize the reflected RF energy by matching the impedance of the plasma to the impedance of the RF energy source. The matching network ensures that the output of the RF source is efficiently coupled to the plasma to maximize the amount of energy coupled to the plasma (e.g., referred to as tuning the RF power delivery) by minimizing impedance mismatch. However, the plasma impedance is not constant and induces variances in impedances that the matching network may not be able to compensate for, reducing the efficiency of the RF energy source.
Accordingly, the inventors have provided improved methods and apparatus for matching impedances between the plasma and RF energy source.